Comment 22 for bug 539426

Maybe I should offer a rationale for wanting the old behaviour back:

All the icons in my gnome-panel behave like this: right click gives a context menu, left click pops up a window or at least some kind of dialogue.
I remember that when a new IM client was introduced (Empathy in 9.10 i think?), the single reason I switched back to Pidgin was that one couldn't easily fix the IMO broken status icon handling.

Last time I looked, KDE panel icons as well as XFCE panel icons behaved "correctly". When I happen to be on a Windows machine, the panel icons also give a context menu on right click and a popup on left click (and sometimes on double click). It can be considered standard behaviour.

IMO it's just intuitive once you've seen a few different UIs, and even more so if you come from only Windows, previous GNOME or KDE.
Fast left click to open the application is like left licking on the window list in the panel to bring something to the front. Crippling the latter functionality by introducing a context menu (on left click) would be very similar to what has been done to Rhythmbox' status icon.